Bytecode decompilation: features and implementation in the blockchain industry
One of the fundamental concepts of blockchain technology is smart contracts — autonomous programs that provide automation and minimize human error. Contracts are written in high-level programming languages that are easy for the developer to understand. To work on the blockchain’s virtual machine, a smart contract must undergo a compilation procedure — a ‘translation’ of the program from a high-level programming language to a low-level language that the virtual machine can understand. The process of decompiling the byte code is the reverse process (reverse engineering process), the procedure of ‘back-translating’ a smart contract from a low-level to a higher-level language.
Application in the blockchain industry
In the blockchain industry, bytecode decompilation can often be the only way to understand the logic behind a smart contract. This is the case for contracts whose owners have chosen not to make the source code publicly available. In this case, decompiling the bytecode will help to understand how exactly the smart contract functions. In addition, decompiling on-chain data helps to be sure that the logic of the exact contract that functions onchain is analyzed.
Benefits of smart contract bytecode decompilation
Investors can benefit the most from decompiling smart contract bytecode, as it can be used to understand what a project’s smart contracts do and how trustworthy the project is.For a smart contract developer, comparing the source code of their smart contract to the decompiled version can help verify that the contract is working correctly.Decompilation is also performed to investigate security incidents or as part of proactive security audits. By reconstructing the operating logic from byte code, it is possible to identify vulnerabilities that have led or could lead to contract violations or loss of funds.Decompiling can also help developers who, for any reason, wish to implement the logic of a particular released smart contract whose code is not publicly available.
Decompilation specifics
The decompilation process is not the most straightforward one. To perform decompilation, one will need more expertise in blockchain development and smart contract security than is necessary to write smart contracts. Although decompilation is a “reverse” process, it should not be assumed that the reconstructed result will be identical to the original smart contract. Decompilation allows to construct the operating logic, but a lot of the abstract information and logic will be organized differently because:
Some of the ‘high-level’ information (such as function and variable names) is simply lost during compilation due to being unnecessary.Bytecode will be decompiled with machine efficiency optimization rather than human understanding. Therefore, although the smart contract will be reconstructed in a high-level language, many operations may be reduced to a form very far from the best practices we are used to encountering.
In general, the completeness of decompilation, in addition to in-depth knowledge of the subject domain, depends greatly on the completeness of the input data, since decompilation can only recover that part of the logic embedded in the input data.
Decompiling and disassembling: what is the difference?
Decompilation is often confused with disassembly. What is the main distinction? Disassembling is a reverse operation on the ‘intermediate level’, when byte code is translated into assembly language, in case of smart contracts it is opcodes. Decompiling, on the other hand, translates bytecode immediately into a high-level language. Disassembling and analyzing opcodes is also a very useful task within the analysis of smart contract work. However, due to the specifics of the ‘reverse translation level’, the decompilation and disassembling concepts are usually distinguished.
Decompilation tools
There are many tools for decompilation, including those in the crypto industry. For EVM-compatible smart contracts, for example, there is an online decompiler on Etherscan (currently running in experimental mode): https://etherscan.io/bytecode-decompiler
Also, a large number of decompilers are available on GitHub. For example, the decompiler used in Etherscan above: https://github.com/eveem-org/panoramix
When choosing a decompiler, it is worth paying attention to documentation, community acceptance, and carefully evaluating the security of the software.
The ethics of decompiling
Many corporations, such as Microsoft, prohibit decompilation of their programs. It is worth considering and assessing the ethics and feasibility of decompiling before starting the decompilation.
Conclusion
Byte code decompilation is an extremely useful technique for analyzing and investigating the code of smart contracts. Along with many other blockchain security techniques, decompilation can reveal vulnerabilities in a smart contract (or lack thereof) and provide insight into the logic behind the contract, all of which is valuable information in the world of crypto.
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Disclaimer
Always DYOR. This article is for informational purposes only, does not constitute legal, financial, investment advice and / or professional advice, and we are not responsible for any decisions based on our analysis or recommendations. Always consult with a qualified security expert and conduct thorough testing before deploying smart contracts.
Bytecode decompilation: features and implementation in the blockchain industry was originally published in Coinmonks on Medium, where people are continuing the conversation by highlighting and responding to this story.